Hydrocarbon Processing - February 2021 - GP-34

BACK TO BASICS

TABLE 2. NGL extraction technologies
Commercial name

Processes

Technology provider

Cryogenic turboexpander technology
CRYOMAX

DCP, MRE, Flex-e

TechnipFMC

High Propane
Recovery

HPA, NGL MAX,
NGL PRO

McDermott/Lummus
Technologies

Gas Subcooled
GSP, SCORE
Process, Single Column
Overhead Recycle

Ortloff

LPG/C3+ and NGL/
C2+ recovery and
STANDARD line

Cry-Plus, ROC,
GSP, RSV

Linde

Cryo-Gas

TCHAP, TRAP, DDP,
VRAP, SARD, ERGR

Fluor

Cryogenic process without expander
Absorption on solvent AET NGL Rec.

Advanced Extraction
Technology

Propane refrigeration
cycle

Open art

Iso pressure open
refrigeration

IPOR

McDermott/Lummus
Technologies

LPG recovery

LPG Plus

Black & Veatch

Joule-Thomson

Open art
Adsorption processes

Generic adsorption
process
Advanced adsorption
process

Open art
ADAPT

Siirtec Nigi through
DNV GL

Absorption on solvent. In this process, a stream of gasoline
(C5+) is used as solvent for extracting NGL in a regenerative absorption process where the raw gas is contacted counter-currently
with a cold lean solvent. The rich solvent drawn from the bottom
of the absorber is regenerated in a fractionation tower and recycled back in the absorber. The refrigeration duties required to
reflux the columns are provided by a propane refrigeration cycle.
Arguably, this process is less efficient and more expensive
relative to the more competitive and simpler expander plant.
This explains why few industrial NGL plants are based on this
technology.
Mechanical refrigeration. In this process, NGL are partially
liquefied by cooling natural gas to a temperature as low as -37°C
to -40°C against an evaporating refrigerant fluid, normally propane, in a kettle-type heat exchanger of a closed-loop refrigeration
system. Part of the refrigeration duty is recovered in the gas-gas
heat exchanger (GGHE), where the raw gas is cooled against the
residue gas from the low-temperature separator (LTS) (FIG. 4).
During the cooling step, the gas crosses the hydrate formation envelope and the risk of heat transfer equipment clogging
increases; therefore, a hydrate inhibitor must be injected upstream of the GGHE. The inhibitor can be either methanol or
glycol-mainly monoethylene glycol (MEG). The former is a
relatively volatile chemical; therefore, MEG is generally preferred to methanol. The mechanical refrigeration is, in practice,
an isobaric process; therefore, it can be implemented only if the
operating conditions fall beneath the cricondenbar.
Joule-Thomson (JT) process. In this process, the gas re34 JANUARY/FEBRUARY 2021 | GasProcessingNews.com

frigeration is achieved by exploiting the cooling effect caused by
the pressure drop across a throttling valve ( JT control valve).
The process scheme is similar to that of mechanical refrigeration. Indeed, in the JT process scheme the mechanical refrigerator is replaced with the JT valve.
As the pressure let down is an isoenthalpic and isoenthropic transformation, the final temperature achievable with this
process is lower with respect to the external refrigeration, but
higher compared to the expander technology. Therefore, the JT
process allows the recovery of a greater quantity of NGL than
the external refrigeration with propane, but a smaller quantity
than the expander.
For tight pressure difference between the raw gas and the
residue gas (the majority of cases), the JT process will eventually
require the installation of a booster compressor to restore the gas
pressure, with sizeable OPEX penalization.
Adsorption on silica gel. Adsorption on silica gel is a separation process (FIG. 5) based on surface chemistry, more specifically on physi-sorption consisting of hydrocarbon and water
bonding on hydroxyl groups distributed throughout the surface
of the silica gel. Being an amorphous material with mesopores of
approximately 20 Å, the pores of the silica gel are also the locus
of C6+ capillary condensation; this characteristic enhances the
efficiency of natural gasoline separation.
By increasing the temperature, the interactions between hydrocarbons and silica gel loosen. After all the sorbent hydroxyl
groups have been engaged and the bed has become saturated,
the adsorbent can be regenerated by heating. Overall, the removal process with silica gel is a dynamic process, where the adsorption stage at temperatures lower than 38°C for a single bed is
followed by a regeneration stage at 230°C-270°C.
A silica gel plant consists of at least one fixed-bed column in
adsorption mode, one in regeneration mode and one in cooling
mode. The continuity of the operation is achieved through sequencing of the columns.
The ADAPT technology utilizes the heat pulse technique,
which consists of heating up only a portion of the bed and then
exploiting the heat accumulated in this portion to heat up the
remaining part of the bed. This technology makes possible the
regeneration and cooling in a single column. In doing so, the
equipment count and the related, costly cyclic valves and headers are considerably reduced, with sizeable CAPEX savings.
Recently, the ADAPT technology has been extensively implemented for dewpoint control for international transmission
of more than 125 Bm3/yr of natural gas through long, submarine pipelines without intermediate recompression facilities.
This process requires deep NGL removal to avoid slug formation in the pipelines. GP
LORENZO MICUCCI is a Senior Director at Siirtec Nigi SpA.
He has more than 30 yr of experience in the engineering and
contracting industry, most of which have been spent in the
natural gas sector. In 2001, he joined Siirtec Nigi in Milan, where
he directed the process design and operations department and
the research and development department. During his time
as R&D head, three patents have been granted to Siirtec Nigi,
two of which have been implemented on an industrial scale. At present, he is the
Senior Director of the technology and marketing departments. Mr. Micucci also
worked for Saipem (Snamprogetti) as a Plant Designer for integrated gasification
combined cycle and gas-to-liquids plants. He holds an MS degree in chemical
engineering from the University of Bologna in Italy and is enrolled as a Qualified
Engineer in the Register of Milan Order of Engineers.

http://www.GasProcessingNews.com

Hydrocarbon Processing - February 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - February 2021